1. Field of the Invention
The present invention relates to a spread illuminating apparatus used as an illuminating means for signboards, various kinds of reflection-type display devices, and more particularly for a liquid crystal display device.
2. Description of the Related Art
A liquid crystal display device characterized by low profile, small occupied volume, light weight, etc. has been extensively used in electric products including mobile phones and personal computers, and the demand therefor has been increased. However, since a liquid crystal of the liquid crystal display device emits no light itself, an illuminating apparatus must be provided when the liquid crystal display device is used in dark places where the solar or illumination light is not fully available. Thus, this illuminating apparatus is also desired to be compact and small in power consumption, and there has been a growing tendency to employ a low profile spread illuminating apparatus of side light type (light conductive member type).
FIG. 5 shows an embodiment of a conventional spread illuminating apparatus of side light type. As shown in the figure, a spread illuminating apparatus 1xe2x80x2 is generally composed of a transparent substrate 2 made of a light-transmissible material and at least one bar-like light source 5 disposed close to at least one of end surfaces 8 and 18 of the transparent substrate 2. The light source 5 is composed of a bar-like light conductive member 3 made of a transparent material and a spot-like light source (for example, a light-emitting diode) 4 disposed facing an end face 7 of the light conductive member 3. Light emitted from the light source 5 is guided into the transparent substrate 2 to irradiate a liquid crystal display device (not shown) disposed under the transparent substrate 2.
A light reflection pattern 49 is formed on an upper surface 46 of the transparent substrate 2. The light reflection pattern 49 is composed of grooves 47 each shaped triangular in section and running parallel to the longitudinal direction of the light conductive member 3 and flat portions 48 each formed between two adjacent grooves 47. The grooves 47 are set to have respective depths different from one another so that light guided in from the light conductive member 3 is reflected in a substantially uniform manner everywhere at the transparent substrate 2 irrespective of the distance from the light conductive member 8 to irradiate the liquid crystal display device (not shown) provided under the transparent substrate 2. Specifically, the depth of the grooves 47 gradually increases in proportion to the increase in distance from the light conductive member 3. The grooves 47 of the light reflection pattern 49 formed on the transparent substrate 2 are very minute and cannot be visually noticeable when observing the screen.
An optical path conversion means 12xe2x80x2 comprising grooves 15xe2x80x2 triangular in section and running parallel to the thickness direction of the light conductive member 3 and flat portions 16xe2x80x2 is provided on a surface 10 of the light conductive member 3 opposite to a surface 9 facing the end surface 8 of the transparent substrate 2. This optical path conversion means 12xe2x80x2 has a function to allow light emitted from the spot-like light source 4 to be made incident on the end surface 8 of the transparent substrate 2 in a substantially uniform manner. The light conductive member 3 is disposed such that the surface 9 thereof faces the end surface 8 of the transparent substrate 2 with a predetermined distance therebetween.
A light reflection member (frame) 13 is provided around the light conductive member 3 in order that light emitted from the spot-like light source 4 is fully utilized to be directed into the transparent substrate 2. The light reflection member 13 is substantially U-shaped in section, disposed so as to cover longitudinal surfaces of the light conductive member 3 except the surface 9 facing the transparent substrate 2 and further the upper and lower surfaces of the transparent substrate 2 at the vicinity of the end surface 8, and is adapted to recover light leaking from the light conductive member 3.
However, with the optical path conversion means 12xe2x80x2 described above, light emitted from the spot-like light source 4 is mostly reflected only at the grooves 15xe2x80x2 to be guided into the transparent substrate 2, irradiating the transparent substrate 2 with many light rays L, and stripe-like fringes appear on a viewing surface as shown in FIG. 6. To overcome such a disadvantage, the applicant of the present invention proposed an optical path conversion means 12xe2x80x3 having grooves 15xe2x80x3 formed with a predetermined inclination angle with respect to the thickness direction of the light conductive member 3 as shown in FIG. 7 so as to increase an irradiation range per groove thereby realizing uniform light emission (Japanese Patent Application No. 2001-287341).
The optical path conversion means 12xe2x80x3 shown in FIG. 7 is effective in softening stripe-like fringes on the viewing surface, but the brightness of the screen decreases due to the inclination angle of the grooves 15xe2x80x3. When the grooves 15xe2x80x3 are shaped substantially triangular or trapezoidal in section, the uniformity of light emission on the screen improves as the inclination angle of the grooves 15xe2x80x3 increases. However, the brightness of the screen decreases as the inclination angle of the grooves 15xe2x80x3 increases, and when the inclination angle exceeds a predetermined value, the brightness of the screen decreases in a greater degree than when a diffusion plate is inserted between the light conductive member and the transparent substrate to improve the uniformity of the light emitted from the screen, which was disclosed by the applicant of the present invention in Japanese Patent Laid-open No. 2000-231814. This comes from that, since the grooves 15xe2x80x3 have flat surfaces, the inclination of the light reflected at the grooves 15xe2x80x3 also increases as the inclination angle of the grooves 15xe2x80x3 increases, thereby reducing the amount of the light reflected at the grooves 15xe2x80x3 which, without repeated reflection in the light conductive member 3, is guided directly into the transparent substrate 2. The light made incident on the surface of the light conductive member 3 at an angle exceeding the critical angle leaks outside, or is reflected by the light reflection member 13 disposed covering the light conductive member 3 to return into the light conductive member 3. In either case, the light suffers loss with the brightness decreased
The present invention has been made in the light of the above problems and the object of the present invention is to provide a spread illuminating apparatus to simultaneously realize uniform and increased brightness over the whole screen.
In order to solve the above problems, according to a first aspect of the present invention, in a spread illuminating apparatus of side light type, comprising a transparent substrate made of a light-transmissible material; and at least one bar-like light source composed of a bar-like light conductive member and at least one spot-like light source provided at an end thereof, and disposed close to an end surface of the transparent substrate, the bar-like light conductive member is a multi-layer light conductive member composed of a plurality of plate-like light conductive members put into lamination, and an optical path conversion means is provided on a side surface of each of the plate-like light conductive members. Since the plurality of plate-like light conductive members having respective optical path conversion means are put into lamination, an optical path conversion means of the light conductive member multi-layered can be constituted by the combination of the configuration of the optical path conversion means of each plate-like light conductive member, thereby diversifying the configuration of the optical path conversion means (hereinafter referred to as xe2x80x9cmultiple optical path conversion meansxe2x80x9d) of the light conductive member.
Further, in order to solve the above problems, according to a second aspect of the present invention, in the spread illuminating apparatus of the first aspect, the optical path conversion means of each plate-like light conductive member is composed of a plurality of grooves and a plurality of flat portions adjacent thereto. In this configuration, the plurality of grooves function as a light scattering part and reflect and guide light from the light conductive member into the transparent substrate.
Further, in order to solve the above problems, according to a third aspect of the present invention, in the spread illuminating apparatus of the first aspect, the optical path conversion means of the plate-like light conductive member is composed of a plurality of grooves with no flat portions. The plurality of grooves function as a light scattering part and reflect and guide light from the plate-like light conductive member into the transparent substrate.
Further, in order to solve the above problems, according to a fourth aspect of the present invention, in the spread illuminating apparatus of the second or third aspect, the grooves of each plate-like light conductive member are formed parallel to a thickness direction of the plate-like light conductive member. Since the grooves formed on each plate-like light conductive member are not inclined with respect to the thickness direction of the plate-like light conductive member, light reflected at the grooves can be efficiently guided into the transparent substrate, and the brightness on a viewing screen is held from degrading.
Further, in order to solve the above problems, according to a fifth aspect of the present invention, in the spread illuminating apparatus of the fourth aspect of, each groove on each plate-like light conductive member is formed to overlap partly with each groove on adjacent plate-like light conductive members such that the grooves on respective plate-like light conductive members as a whole constitute grooves (hereinafter referred to as xe2x80x9cmultiple groovesxe2x80x9d) of the multi-layer light conductive member, which are inclined with respect to the thickness direction of the multi-layer light conductive member. With this structure, the bright portion of light reflected at each groove on each plate-like light conductive member overlaps partly with the bright portion of light reflected at each groove on adjacent plate-like light conductive members, whereby the bright portions of light guided into the transparent substrate from the multi-layer light conductive member can be continuous with one another with respect to the longitudinal direction of the light conductive member.
Further, in order to solve the above problems, according to a sixth aspect of the present invention, in the spread illuminating apparatus of the fifth aspect, the multiple grooves are formed such that each thereof overlaps partly with adjacent ones with respect to the longitudinal direction of the light conductive member. With this structure, the bright portions of light reflected at each of the multiple grooves overlaps partly with the bright portion of light reflected at adjacent multiple grooves, whereby the bright portion of the light guided into the transparent substrate from the multi-layer light conductive member can be continuous with one another across the transparent substrate.
Further, in order to solve the above problems, according to a seventh aspect of the present invention, in the spread illuminating apparatus of the fourth aspect, each groove on each plate-like light conductive member is formed not to be aligned to each groove on adjacent plate-like light conductive members. With the structure, each light reflected at the groove can be spread at equal intervals entirely over the transparent substrate, thereby making bright and dark fringes generated on the transparent substrate less noticeable
Further, in order to solve the above problems, according to an eighth aspect of the present invention, in the spread illuminating apparatus of the second, third, sixth or seventh aspect, the grooves on the optical path conversion means of the plate-like light conductive member are triangular in section. Further, according to a ninth aspect of the present invention, in the spread illuminating apparatus of the second, third, sixth or seventh aspect, the grooves of the optical path conversion means of the plate-like light conductive member are trapezoidal in section. With such configurations, the grooves function as a light scattering part to reflect and guide light from the light conductive member into the transparent substrate.